Dual-fuel engines, also referred to as bi-fuel engines, are internal combustion engines that operate on both a gaseous fuel and diesel fuel simultaneously. A common gaseous fuel for dual fuel engines is natural gas.
Typically, the diesel fuel is essentially for ignition; it auto ignites under compression and its combustion ignites the natural gas. Use of the diesel fuel retains the benefits of a diesel compression ratio and its efficiency, while use of the natural gas contributes to lowered emissions and fuel costs.
Natural gas can be introduced to the combustion chamber by either mixing it with the airflow or injecting it directly into the chamber. In a “fumigation” process, natural gas is mixed with air, and both enter the combustion chamber together in a desired proportion. In direct injection, the natural gas is introduced into the chamber just prior to burning.
A known issue with all gaseous-fueled engines, including dual-fuel engines, and especially those with fumigation-type or other “upstream” injection of gas, is poor transient response. This is due to the transport delay from the gaseous fuel injection point to the engine cylinders. This delay can result in slow up-transients as well as slow down-transients.